(1) Field of the Invention
The present invention relates to a pneumatic radial tire superior in its service life.
(2) Description of the Prior Art
Over the years, radial tires have been widely used, each which includes a carcass body consisting of ply cords substantially radially arranged in the tire and employs a belt consisting of a plurality of laminated plies whose cords intersect each other and surround the carcass body as a reinforcement of a crown for the purpose of supporting circumferential components of pneumatic pressure in the tire. The belt of such a tire is generally required to have a high rigidity.
However, as the rigidity of the belt becomes higher, shearing strains between the laminated plies at edges of the belt will be greater which tend to shorten the service life of the tire.
Accordingly, the belt is required to have a high rigidity for supporting stresses resulting from the inner air pressure of the tire, while at the same time it is important at its edges to have a characteristic which reduces the shearing strains between the laminated plies rather than the high rigidity. In other words, the belt is required to have the different properties at the respective central and edge zones of the belt.
The prior art, however, is devoid of a radial tire having this consideration of the belt's rigidity to match the above requirement.